The present invention relates to a laser device used in an optical information recording/reproduction apparatus and, more particularly, to a stabilized laser device in which output light is automatically controlled and stabilized at a desired level.
An optical information recording/reproduction apparatus has two operation modes (i.e., recording and reproduction modes). To read data from a recording medium (e.g., an optical disk), the apparatus is set in the reproduction mode. To write data on an optical disk is supplied, the apparatus is first set in the reproduction mode. The apparatus radiates a laser beam of a predetermined intensity (hereinafter called reproduction level) to read the address of the track, obtained in accordance with the reflected light therefrom. A head is then moved to a track corresponding to a write address. Thereafter, the apparatus is switched to the recording mode, and data is written at the address. For example, "1" data is written such that a laser beam of great intensity (hereinafter called recording level, normally several times higher than the reproduction level) is radiated on the disk to form pits in the disk surface. Since "0" data is written so as not to form pits on the disk surface, the laster output is switched to a low output (reproduction level). For this reason, output beam of a laser device used in the optical information recording/reproduction apparatus must have two different output levels.
In general, semiconductor laser output varies widely in accordance with environmental factors (e.g., ambient temperature). The semiconductor laser output also varies widely in accordance with self-degradation. For this reason, a device for stabilizing laser output and improving reliability is necessary for a semiconductor laser apparatus. A conventional semiconductor laser stabilized device used in an optical information recording/reproduction apparatus has been proposed in Japanese Patent Disclosure No. 58-158051. In this device, feedback control is performed by obtaining the difference between a detector signal from a photosensor and a reference signal in the reproduction mode, while open-loop control is performed in the recording mode. In the reproduction mode, a laser drive current is sampled and held and in the recording mode, the sum of recording data and the hold signal is used as a laser drive current. However, the conventional apparatus cannot cope with wide variations in ambient temperature in the recording mode.